The need for small, fast, and sensitive detectors of biological agents which are able to continuously monitor an environment for extended periods of time is underscored by the proliferation of biological and chemical weapons, the poor man""s nuclear weapon. Under battlefield conditions, a useful detector would rapidly alert a soldier when a specific biological or chemical agent is detected so that countermeasures can quickly be implemented.
Such detectors would be useful in non-military applications as well. Rapid detection of antibiotic-resistant bacteria in a patient would help clinicians select a more effective therapeutic regimen. Continuous monitoring of a city""s drinking water supply would provide early warning of potential pathogens, giving public works officials more time to manage the potential health risks to the public. In addition, the use of these detectors in meat and poultry inspections would be a significant improvement over the current xe2x80x9cpoke-and-smellxe2x80x9d procedure.
All vertebrates acquire a specific immune response to a foreign agent (antigen) in part by generating an immense diversity of antibody molecules. Antibody molecules bind to antigen with high specificity, e.g., they can differentially bind to two closely related strains of bacteria or viruses.
Antibodies are produced by B cells, a crucial component of the immune system. An antigen can activate a B cell by binding to antibodies on its surface, leading to a cascade of intracellular biochemical reactions which causes a calcium ion influx into the cytosol of the B cell.
For a review of antibody structure and function and B cell activation, see Paul, editor, Fundamental Immunology, 3rd ed., Raven Press, New York (1993).
This invention relates to a device for detecting an antigen. The device includes a liquid medium containing cells (e.g., a B cell or fibroblast) and an optical detector, the liquid medium receiving the antigen. Each of the cells has antibodies (e.g., chimeric or single chain antibodies) which are expressed on its surface and are specific for the antigen to be detected. Binding of the antigen to the antibodies results in an increase in calcium concentration. The cells also contain emitter molecules (e.g., aequorin or indo-1) in their cytosol which emit photons in response to the increased calcium concentration in the cytosol. The detector can be separated from the medium containing the cells by a covering (e.g., glass) that is transparent to the photons. Such a covering can serve to support the medium, protect a fragile surface of the detector, or be used as a lens. The optical detector, e.g., a charge-coupled device (CCD) is able to detect the photons emitted from the cells in response to the increased calcium concentration and indicate to the user that the antigen to be detected is present. Other optical detectors which can be used in the device include a photomultiplier tube or a photodiode. In some embodiments, the optical detector is able to distinguish individual cells.
The device can be contained within a housing made from, for example, aluminum, plastic, or stainless steel. Such a housing can prevent contamination of the device with extraneous organisms. The housing can include two halves attached to each other on one side of the housing by a hinge joint. In applications where an airborne antigen is to be detected, the housing can contain one or more openings for the antigen to pass into the device. Such an opening can be screened by an antigen-permeable barrier such as a metal mesh or a membrane.
The sample containing the antigen can pass through a filter before the antigen contacts the cells. Suitable filters include passive filters (e.g., filter with determined pore sizes, affinity columns or immunofilters) and active filters (e.g., fluorescence-activated sorters, active size sorters, or microfluidic systems).
The invention also features a method for detecting the presence of an antigen, which includes providing a sample (e.g., a volume of air) suspected of containing the antigen; introducing the sample into a device containing cells immersed in a medium; and monitoring photon emission as an indication of whether the antigen is present. The cells used in this method are described above.
Further, the invention includes a cell containing an emitter molecule and having antibodies on its surface, so as to be useful in the devices and methods of the invention.
Other features or advantages of the present invention will be apparent from the following drawings, detailed description, and the claims. Any publications cited in this disclosure are hereby incorporated by reference.